1. Field of the Invention
The present invention relates to a lens plate capable of removing stray light, a method for manufacturing the same and an image transfer device for transferring an image to a linear image formation area using an erecting lens array formed by combining lens plates.
2. Description of the Related Art
An optical system of a device for reading an image includes a reducing system and a unit magnification system. A lens array to be used in a unit magnification system is an erecting unit magnification lens array and ordinarily has several rows of rod lenses defined herein as lens rows arranged along a long-side direction of the lens array (in a main-scanning direction of an image reading device). Although it is possible to improve the transferability of a light quantity and reduce an unevenness in quantity of transmitted light by increasing the number of rows of lenses, the number of lens rows, in general, is one factor in in consideration of a manufacturing cost for a lens array using rod lenses.
On the other hand, an erecting unit magnification lens array can also be formed using a resin lens plate having a plurality of convex micro-lenses arranged on its surface. A lens array using such a resin lens plate provides an advantage of enabling a lens array having a plurality of lens rows to be manufactured at a comparatively low cost.
However, since an erecting unit magnification lens array using a conventional resin lens plate does not have a wall for shading a light beam between lenses adjacent to each other, there is a problem of stray light that a light beam obliquely entering a lens plate obliquely proceeds through the plate, enters an adjacent convex lens and then exits the lens to form a ghost image.
There are known methods to counter such stray light. One method of forms a light shading layer between adjacent lenses. A method forms a light shading layer between lens plates arranged opposite to each other. A light shading layer may be formed by means of a photolithography process using a photoresist containing a light absorbing agent. Another method forms a light shading layer by applying a light absorbing paint to the whole surface of a lens face and removing only the light absorbing paint on the lens part. A further method forms a light shading layer by applying a light absorbing paint to a part on which a light shading layer is to be formed by means of an ink-jet printing method. Another method forms a light shading layer by forming a groove in a part on which a light shading layer is to be formed and filling this groove with, for example, a light absorbing paint.
The formation of light shading layers around lenses, between adjacent lenses and between lens plates arranged opposite to each other is effective for removing light coming in from outside of a lens area or removing light obliquely entering a lens and exiting from the outside of a lens area. However, the light shading layers cannot remove stray light formed by light obliquely entering a lens, passing through a lens plate in the direction of a thickness of the lens plate and exiting from the exit side of a lens adjacent to that lens.
In the case of forming a light shading layer by forming a groove and filling the groove with a light absorbing paint, the groove may be formed by means of a transfer molding method using a metal mold. A light shading film may be formed on side faces and a bottom face of the groove. The depth of the groove is limited by the formability of a lens shape or the releasability of a lens plate from the metal mold. Therefore, it is difficult to obtain a groove having an aspect ratio necessary for forming a light shading layer necessary for removing stray light formed by light obliquely entering a lens, passing through a lens plate in the thickness direction of the lens plate and exiting from the exit side of a lens adjacent to that lens.
Therefore, an erecting unit magnification lens array using a conventional resin lens plate still has a problem in that it cannot sufficiently remove stray light, makes a ghost image and is inferior in resolution.
An object of the present invention is to provide an erecting lens array capable of sufficiently removing stray light.
Another object of the present invention is to provide an image transfer device capable of sufficiently removing stray light in using an erecting lens array.